This invention relates to an area exposure apparatus and method for exposing an area of text on a recording carrier. More specifically, the invention relates to a device and method which converts text data into signals useable by a scanner to expose the text on the recording carrier.
In this text, the term area exposure apparatus mounted together with a laser recorder is intended to means, as known to those of ordinary skill in this art, either laser printers which produce a final printed product or laser typesetting apparatus or devices, which produce a typeset product, i.e., a typographically typeset text, which has to be transferred by further techniques onto a printing mold, particularly, a printing plate. Laser printers and laser typesetting devices differ from each other essentially in that the latter typeset typographic characters with a high resolution than is possible with the laser printer is printing. As for the details of operation, the essential structures, of interest in the present case, are similar in laser printers as compared to laser typesetting devices.
Area exposure apparatuses of the type discussed above are generally characterized in that they do not build up the characters individually, one after the other, with the exposure of the individual characters being performed by means of a raster scan at right angles relative to the line direction of movement of a carrier being exposed. Instead, after the termination of a scan line, the recording carrier upon which the exposure is made is continuously moved in a forward move direction at right angles relative to the line direction, with this forward more direction being synchronized with the deflection movement of a scanner, and with the scanner scanning the recording carrier along horizontal scanning lines over the width of a plurality of characters, particularly of all the characters of a specified line of text.
Prior art area exposure apparatusses include as the scanner a polygon mirror, which rotates at a high speed of rotation and deflects an intensity-modulated scanner beam at right angles relative to the forward move direction of a recording carrier, i.e., a film. Between two subsequent scanning lines, the recording carrier is continuously transported to a given height. The deflection movement projection upon the recording carrier extends in this case over at least the so-called typesetting width which is scanned by the scanner beam and is image-wise exposed over a width corresponding to the text line to be exposed. In view of the high speed of the scanning movement and of the relatively high forward move speed, high typesetting speeds are obtained, for example, by a device such as commercially under the name "Linotron 600" from Linotype GmbH. This is at least true if the line width to be exposed is not substantially narrower than the typesetting width.
If, however, text columns have to be typeset which are narrow relative to the typesetting width, a large portion of the projected deflection movement extends needlessly over the recording carrier because during a great portion of the scanning movement, image-wise exposure does not take place. Because the forward movement of the recording carrier coupled to the scanning movement remains essentially constant, the same time is needed for the exposure of narrow lines as for the exposure of broad lines. In this case it is assumed that by means of an output data processing system of the area exposure apparatus, output data for the control of a modulator of the scanner beam from received text data and character-specific data is so rapidly generated and stored that the forward movement sychronized with the scanning movement need not be stopped even in case of great line widths of the text to be exposed. The generation of such output data which includes the modulation, or the switch-on or switch-off, of a scanner beam, respectively when scanning along the scanning lines, constitutes the general background state of the art such as disclosed German Patent Specification No. 2,940,897, the disclosure of which is specifically incorporated by reference herein, and according to which output data, so-called third digital data, giving the interfaces of the contour lines of a plurality of characters with one raster line, i.e., a scanner line, each are stored in the raster line storage buffer or buffers.
From these so-called third digital data, a video control signal is generated, which switches the scanner beam on and off by means of a modulator. The deflection of the beam for scanning the recording carrier is, in that case, performed by means of a resettable mirror which is moved, at an essentially constant angular velocity, in one direction whereupon the mirror is rapidly reset into the starting position and the scanning process is repeated after the next trigger pulse has been received.
In addition to the resultant relatively low typesetting speed when exposing narrow text columns with a constant typesetting width with continuous coupled movements of the scanner and of the drive means for the recording carriers forward move, the material of the recording carrier is made little use of if only one long column along one length section of the recording carrier is exposed.
It has therefore also been known to provide an area exposure apparatus of the kind mentioned above as the "Linotronic 600", with a converter, which converts the text data of a narrow text exceeding a given length to width ration into converted text data of a text occupying a larger width of the recording carrier. To this end, the text is segmented along section lines in the direction of the line, and the relatively short text segments are exposed, one next to the other, on the recording carrier. As a result, scanning and exposing is performed along a scanning line over the width of a greater number of characters. It is in this environment, however, that a disadvantage results in that, subsequently, the text segments have to be mounted together by hand. When relatively short text segments are concerned, the mounting work hinders obtaining the advantage of a higher exposure speed.